The proposed project explores ways of analyzing statistically the patterns of interaction between mother and infant, as they develop and change from the 3rd day to the 3rd month of life. It aims at an analysis that explains these differences as a function of (a) maternal expectations and attitudes, (b) the differential responding by the infant to maternal behaviour (c) the differential responding by the mother to the infant's behaviour. The study investigates, primarily, the increased differentiation in interaction patterns between mother and infant as a function of the child's age and sex as well as mother's ethnic and socio-economic background. This interaction is also studied in relation to various attitudes and practices as expressed and described by the mother during short, structured interviews. In addition, the interaction is studied in relation to aspects of the infant's behaviour outside the interaction with the mother, and to aspects of the child's inanimate environment. The main body of data collected is based on direct observations of 64 infants during 3 periods of interaction with their mother: The first observation is during breast-feeding, at 3 days, the second at the age of 30 days and the third at 3 months. The behaviour of both mother and infant is simutaneously recorded every 5 seconds on a pre-defined checklist of behaviour categories. Individual differences in interaction, found at the age of 3 days reflect on the mother's part her behaviour style, preferences and attitudes and on the infant's part his temperamental characteristics and whatever other biologically determined response hierarchy he may bring with him into the maternity ward. The other observation periods reflect the results of the process of the mutual learning of response hierarchy of both partners as well as the adaptation to the quickly changing response repertoire and needs of the infant. The analysis of the differential responding at a given interaction period should enable us to predict individual differences in the following period.